Process for the manufacture of microporous rubber compositions



Patented Oct. 26, i937 I 1 UNITED STATES PATENT OFFICE PROCESS FOR THEMANUFACTURE OF MI- CROPOROUS RUBBER COMPOSITIONS William J. Burgess,Palmyra, N. .L, assignor: to Q 7 The Electric Storage Battery Company,Philadelphia, Pa., a corporation of New Jersey No Drawing; ApplicationMarch 30,- 1934,

Serial No. 718,209

9 Claims. (Cl. 18-53) This invention relates to the production of costthan that attained by otherprocesses with microporous diaphragmssuitable for use as filwhich I am familiar.

ters or as separators for storage battery cells. The proportions givenin the following ex- Several methods have heretofore been proamples areby weight and not by volume. posed for the production of porous materialcom- As an embodiment of. this invention in its 5 posed of vulcanizedrubber or the equivalent with simplest form, the following formula isgiven: 1. or without the admixture of inert fillers in pow- Parts deredform, the product being permeated by 1 Rubber ,25 minute pores ofmicroscopic dimensions render- Sulfur 1o ingit'suieble We as afilierorapmus Beatriz;312:::::::::::::::::::::::::::1 65

phragm in an electrolytic cell such as a storage battery. In all ofthese previous disclosures the Mix on a mill, calender to shape, andvulcanize rubber is introduced either in the form of a soluunder wateror in an atmosphere of steam, with tion or an emulsion (rubber latexbeing an exor Without previous soaki i Wa er.

151: ample of the latter), or is t o ta bjected Cellulosic fibers may besubstituted for bento- 5 to the action of a solvent. nite, these fibersbecoming comminuted to a finely I have discovered that a similar,microporous, divided state in the milling of the material. rubberproduct having the characteristic of ionic As an embodiment using gelsof the silica type, permeability recognized as essential to a successthefollowing procedure is suggested:. 20 ful battery separator may beproduced from gum Part 20 rubber without the necessity of passing itthrough Rubber the condition of solution or emulsion or subject-- Sulfur1Q ing it to a solvent. This result is accomplished Powdered sodiumsilicate 65 by processing the gum rubber with fillers of a 5 certzimfiefimte type P of swemngi by acid, or a salt solut1on whereby thesodium siliapphcation of water, in a manner analogous to cate istransformed to gel, and vulcamze under standard rubber procedureinvolving mixing, Water or in an atmosphere of Steam fiz gg and Shapmgby calendermg a The procedure may be varied to include'the' The fillersemployed in my process are those mlxmg of two or more of the speclalfillers ferred to, such as clay silicate gums or cellulosic having thecharacteristics of hydrophilic colloids V as described by the Bureau ofStandards, Techfibers m wet state m any proportions drymg said mixture,and pulverizing said mixture. As nical Paper #438. They have a strongaffinity an embodiment using this method, the following for water withwhich they appear to comblne procedure is suggestedz. V 7

Mix on a mill, calender to shape, soak in a dilute either by adsorptionor in other ways not fully .35 understood. These fillers include suchdiversi- Rubber Parts fied products as clays of the bentonite or zeoliteSulfur type, artificial zeolites, such as permutit com- Dry pulverizedmix t: 65

minuted and thoroughly pulverized cellulosic 40 material, gums capableof forming a gel with Mix on a mill, calender to shape, vulcanize in an40 water, such as tragacanth, agar-agar, karaya, atmosphere of steam orunder water, with or and gelatin, and gels of the silica type, added aswithout previous soaking in water, dilute salts, or such or formed insitu. These hydrophilic coldilute acids. loids may be divided into twoclasses. In the The exact theory, as to how the microporous case of thegels, the Water is taken up by the structure is developed in the processdisclosed substance itself, causing the individual particles above, isnot thoroughly understood. It is beto swell. In the case of the clays,the water is lieved to be brought about by the penetration of attractedto the surfaces of the particles and aqueous moisture through theexceedingly thin adheres as a film, causing an apparent andequivmembranes of rubber surrounding the particles alent increase in theparticle size. The mixture of filler. The taking up of this moisture bythe 50 of rubber and filling material of the class departicles of fillercauses a swelling of the entire scribed is vulcanized under water or inan atmosmass, putting the rubber films under tension. phere of steam.The product thus produced The vulcanizing process causes a hardening ofpossesses properties enabling its use as a porous the rubber and areduction of its elasticity, thus diaphragm in electrolytic cells and ata lower causing disruption of the rubber membranes.

the porosity and strength desired: in the final l at preliminary soakingprior to vulcanization will depend upon the particular type of fillerused and product. I

'Ildo not intend tobellimite d save as the scope of the prior art and ofthe attached claims may require. V

I claim: 7 7 i 1. The process of makingamicroporous diaphragm whichconsists in plasticizing by means of repeated and continuous milling ,anadmixture of unsoitened gum rubber in a solid state" andardryhydrophilic colloid capable oflswelling when wet with water and avulcanizing agent, mechanicallyv shaping the plasticized mass, swell ingthe colloid particles and putting the rubber; in tension by subjectingthe shaped mas's' tothe action j'ofwater, and'hardening and disrupting;

the rubber from a state of tension by vulcanizing the mass in contactwith moisture thereby pro,

viding microporosity. r

2. The process of 'makinga microporous dia-' phragm which consists inplasticizing by' means of repeated and continuous mi11ing;an admixtureof unsoftened gum rubber 'in a solid state and a dry hydrophilic colloidcapable of swelling when wet with Water and a vulcanizing agent,mechanically shaping the plasticized mass, and

V swelling the colloid particles and disrupting and 1 withgum rub berand sulphur with a sulphur-I hardening the rubber by vulcanizing themass in contact with: water moisture thereby providing microporosity. vV

3. The method of .:making a micro-porous, chemical-resistant, semi-rigiddiaphragm, which comprises, mixing dry fibrouscellulosic material rubberratio suitable for vulcanization to hard rubber, plasticizing the rubberby means of re peated andcontinuous milling, therebyjcomplete- 1ygrinding the fibrousjing'redients to colloidal dimensions, mechanically"shaping the plasticized.

mass, andyulcanizing under water.

, 4. The, method of Vma'kin'g a 'micro-porous; 7 chemical-resistant,semi-rigid diaphragm, which. comprises, mixing dry fibrous cellulosic.material with gum rubber andsulphur with a sulphur rubber ratiosuitable for vulcanization to hard rubber, plasticizing the rubber bymeans of repeated and continuous milling, thereby completely grindingthe fibrous ingredients to colloidal dimensions, mechanically shapingthe plasticized mass, and vulcanizing in an atmosphere of steam.

' 5. The method of rmaking a micro-porous} chemical-resistant;semi-rigid sheet material, which comprises, mixing dry clays of thebentonite or zeolite type with'gum rubber and sulphur, plasticizing byrepeated milling of the mix,

shaping, and *thenmoistening and vulcanizing in the presenceof moisture.

' 6. The 7 method of making a micro p orous,

chemical-resistant, semi-rigid sheet material, which comprises, mixing"dry clays of the bentonite or zeolite type with gum rubber and sul phur,plasticizing by repeated milling of the 'mix,

o shaping, soaking in water, and vulcanizing in thepresence of moisture.7. The process of making a micro-porous, chemical-resistant, semierigidelectrolytic diaphragmhaving ionic permeability which processcomprises-mixingon a mill in a dry. state an admixture of gum rubber ina solid and unscitened stateand a dry hydrophilic colloid capable ofswelling when wet with water and a vulcaniza ing agent,mechanicallyrshaping the admixture,

swelling the colloid'particles and putting the rubher in tension bysubjecting the shapedlmass to the action of water, and hardening anddisrupt ing the rubber from a state of tension by vulcanizing the massin contact with moisture thereby providing microporosity. V p

8. The method of making a microporous chemically resistant semi rigidelectrolytic diaphragm having ionic permeability which-comprises mixingin a dry state a hydrophilic colloid with gum rubber and sulphur inaproportion suitable for vulcanization to hard rubber, mechanicallyshapring the mass, subjecting the mass to aqueous moisture, andvulcanizing in the presencerof moisture. l.

9. The process of making a semi-rigid micro-, porous electrolyticdiaphragm having ionic'permeability which includes the steps ofpreparing a dry admixture of a finely divided hydrophilic substancewithrubber and sulphur in 'a propor-' 'tion; suitable for: vulcanizationtohard rubber,

mechanically shaping the mass while inthe dry state, subsequentlyswelling the hydrophilic particles by subjecting the mass to aqueousmoisture,

V andthen setting the binder by the application of heat in the presenceof moisture. j V V WILLIAM J. BURGESS.

